Hi Stéphane Well... just got done re-reading Rons article and as I understand it turns out that Terry's answer really is wrong on two counts and perhaps (probably right) on the third. As to the conclusion as to whether its a good idea to dry the ribbed assembly down before gluing into the rim... lets just say whatever reason there is for that doesn't seem to have much to do with creating or supporting crown.... tho I still have a bit of reserve head scratching to do on that matter. Ron does two things in his experiment. The first more or less proves the end grain is substantially more tough then this idea that it will just crush under pressure idea that has been thrown around. He constructs a small single ribbed panel, dries it down and wedges it into small base and buttress jig made from old pinblock material. The sides of this panel would not be able to move outwards period. Upon taking on humidity the thing even after a few weeks took on no crown. The reason given has to do with the geometry of buttressed arches... and if correctly assessed (and I see no reason to doubt his assessment) a direct consequence is that the edge wood of the top half of this little panel did not crush despite the pressure it was under. The only thing I can see possibly going wrong in this part of his experiment is that it appears in the foto that the underside of the ribs were flush with the base of the jig... which may have influenced the lack of appearance of crown... but I kinda doubt it. Still... I suppose I'd like to repeat his experiment without that "constraint". In any case all this kinda shoots the sh#t out of the crushed edge argument. The next part of Rons experiment was simply to demonstrate that there is no outwards pressure on the rim... or in the case of his experiment his base and buttress jig when a ribbed and crowned panel was placed into it.. and wedged tightly as before. What happens when downbearing is applied.... is that the edges actually pull away from the <<rim>>. So Terrys comment below was wrong on both the first two counts. The top edge wont crush to begin with, and the top edge doesn't expand outwards to begin with. At least not in the face of an increase in down bearing... and all of this is well justified by the same geometry relating to buttressed arches as above. Anyone re-reading the article will be able to see this readily. As for the rim in a real piano being resistive enough... well... Rons experiment doesnt really get into that. And in my mind there are a couple questions left open about what happens to an already crowned panel that actually does expand outwards against a resistive ridge... Perhaps it will behave exactly the same as the flat panel in his experiment... I just haven't thought it through enough yet. In anycase... whatever reasons there are for drying out the panel... and fitting it tightly to the rim before letting it take on humidity do not seem to me to have much to do with the crowning issue. Then there was JD's post which I am still in my mind trying to fit into this picture. I'm not sure what he was saying there... but it seemed like he was stating that a rib crowned panel glued into place would if anything move in the direction of reverse crown upon taking on humidity. Much of the middle part of the rib was above his two <<force lines>>... and a panel taking on humidity along with that part of the rib would all want to expand... Putting the rest of the rib under some tension.... How that could result in a kind of reverse crown strain I dont see at this point...and perhaps thats not what he was saying at all. But if so.. then how that in turn would affect whether the edge grain of the panel would be exerting outwards pressure on the rim or pulling away as in Rons demonstration... well all this has my head aching again :) Actually... I love it.... wish I knew more and wish this medium of ours allowed for better communications among folks who clearly share an awful lot of the same kinds of interests but dont seem to manage to get across to each other. To end... I'd say the most obvious relavant thing I've seen in these posts that have tried to address your question is that a tighter fit probably results in less movement.. or wiggle someone said in the position of the soundboard... and hence bridges with changes in humidity.. which gets into all kinds of other stuff... your glue questions for one... Hope this all serves to yield a nice evenings sleep :) Cheers RicB Hi Terry (and Mike, and Ric). If I get you all right, there is no need for drying the ribbed panel again before gluing it in the piano. But then, if I understand well, there would be no problem either gluing the ribbed board in the piano in a 60 % humidity environment, and let the piano undergo severe winters at 28 % either. Is this what you think ? If so, I have to admit I must update my own thoughts (which happens often these last days), for example about soundboard cracks causes. So all the climate matters are between the ribs and the board (and the method of assembling), right ? By the way, my miserable board did come back to normal shape (after 48 hours) and is glorious again. I see no reason anymore to commit suicide today. Best regards. Stéphane Collin. 'Course, none of this actually works - the ribs won't shrink much, the panel top edge will just crush when it expands the 1/10 mm that it might move and the rim has enough flex to negate any "arch" support. Terry Farrell
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